Characteristics of Diagenesis and Its Control on Tight Sandstone Reservoir of Yanchang Formation in Luohe Block of Zhidan Oilfield, Ordos Basin

The tight sandstone reservoir of Yanchang formation in Luohe block of Zhidan oilfield in Ordos basin has strong heterogeneity, complex pore structure and various diagenesis types, which leads to unclear understanding of the temporal and spatial distribution law and main controlling factors of Yanchang formation tight sandstone reservoir. This paper makes an in-depth study on the diagenesis of tight sandstone reservoir and its relationship with reservoir physical properties by means of core observation, thin section identification, scanning electron microscope analysis, X-ray diffraction analysis, physical property test, mercury injection test and mathematical statistics. The results show that the diagenesis of tight sandstone reservoir of Yanchang formation in Luohe block of Zhidan oilfield is varied, including compaction, cementation, metasomatism and alteration, recrystallization and dissolution. Compaction is the main reason for the deterioration of tight sandstone reservoir physical properties. The early carbonate cement content has obvious destructive effect on the reservoir physical properties when it’s more than 6%, but also can improve the compaction resistance to protect the reservoir when its content is less than 6%. The late carbonate mineral cementation mainly destroys the reservoir. Siliceous cement also can protect reservoir when its content is low, but with the increase of it, the reservoir physical properties obviously become worse. Recrystallization further destroys reservoir quality, while dissolution obviously improves the physical properties of tight sandstone reservoir.